Continuous ink jet printheads utilize a series of orifices separated from charging leads by a small gap. Fluid is forced through the orifice while the printhead is in operation. Upon shutdown, the ink floods the leads and the area around the orifices. This fluid then dries, leaving behind non-volatile components in the form of solids or gels. Depending on the ink chemistry, this ink may polymerize as it dries, rendering it insoluble. Upon subsequent startups, the failure to remove or redissolve all of this material in the orifice and gap creates disturbances in the shape or direction of the emerging jet. Heavy deposits may block the orifice altogether. Deposits left on the charging leads may leave films which impair the proper charging of the drops as they form, causing insufficient deflection of the drop.
Current ink jet systems consist of a fluid module with a removable printhead. In the course of operation it may become necessary to move a printhead from one system to another. Ink residue remaining in the printhead from the previous system may contaminate the second system if the ink color or chemistry is incompatible.
This problem has been addressed in the prior art. For example, U.S. Pat. No. 5,706,039 distributes a cleaning fluid externally, in the plane of the orifices, not through them. This requires the use of a two layer construction, or forming internal passages within the orifice plate. The vacuum used to remove cleaning fluid in the vicinity of the orifice may also carry external debris into the orifices. U.S. Pat. Nos. 5,570,117 and 5,555,461 utilize wipers to remove ink from the orifices, with no additional cleaning fluid used. U.S. Pat. No. 5,557,307 uses a cleaning thread to wipe the orifices. Ink is adsorbed onto the thread, removing it before it dries.
Unfortunately, mechanical devices such as wipers and thread need replacement or maintenance from time to time and may serve to push particles into the orifices. It is seen, then, that there is a need for a system and/or method for cleaning a printhead which will avoid the problems associated with the prior art.